Implementation science is key to understanding how interventions, programs, and other practices are integrated into routine practice across diverse settings. This chapter presents a taxonomy that categorizes five types of theoretical approaches used in evaluating the implementation of health service practices: process models, determinant frameworks, classic theories, implementation theories, and evaluation frameworks. Process models guide the stages of translating evidence into practice, while determinant frameworks highlight factors that influence outcomes. Classic theories from other disciplines and implementation theories developed within the field explain causal mechanisms of change. Evaluation frameworks identify aspects of implementation that should be assessed to determine success. These approaches are crucial for evaluating health service interventions and programs, providing structured methods to operationalize and measure factors influencing implementation success.